A description of the sound of the Woo sounds like an audiophile rave checklist. It is transparent, particularly in that you don’t notice any treble veiling or grit as you do with some lesser headphone amps. Bass is solid, well defined and can be very deep with the right headphones. Tonal balance is very, very good, with no sense of treble roll-off or brightness.
This is one of those difficult-to-review products because it is hard to find deficiencies. Perhaps there is an even better headphone amp, and I’ll be back to explain problems with the Woo. Perhaps as D/A converters get better, distortions in the WA22 will be revealed. But right now, these problems are below the error noise floor in most cases. Maybe even more important, the errors in headphones are much, much greater than any you’ll find in the WA22.
I tested the Woo with a wide variety of headphones, including the Sennheiser HD800 and HD650, the Grado PS1000 and 325is, the Ultrasone Edition 8 and the Denon AH-D5000. This is where things got interesting. In 90% of these cases, I thought the mid-range was slightly more present and vivid with the WA22 than with the other headphone amps I had on hand. The effect I’m talking about doesn’t sound like a frequency response bump, but rather like an increase in midrange contrast (the analogy here is to images, where contrast is a separate factor from color or resolution). Another way of expressing this is to say that micro- and macro-dynamics in the mid-range were slightly better with the WA22 than in other top-tier headphone amps I’ve heard thus far. This generally made each headphone sound more realistic and more like live music.